This invention relates to lamps and more particularly to motor vehicle headlamps.
The sealed beam headlamps that were mandated in the U.S. in 1939 are now being replaced by replaceable bulb headlamps which offer more styling freedom and allow for the myriad of exotic headlamp shapes that have appeared in the last several years. However, the replaceable bulb headlamps require a separate lens and reflector and therefore require a seal at the interface of the lens and reflector. As the lamp is turned on and off the temperature inside the lamp and therefore the pressure increases and decreases and this over a period of time has the effect of fatiguing the seal with the result that the seal leaks and moisture is sucked into the headlamp. The moisture attacks the reflective surface and also forms beads on the inside of the lens which undesirably varies the optical light pattern of the lamp. In an attempt to maintain a substantially constant pressure within the lamp and thereby avoid the seal fatigue, vents have been provided in the reflector to maintain a substantially constant pressure within the reflector. However, the vents must be carefully placed and, specifically, a first vent must normally be provided in the low pressure region of the reflector and a second vent must be provided in a high pressure region of the reflector. However, the locations of the high and low pressure vents cannot be determined until the lamp has been designed and tested in actual usage in the field. The headlamp unit must then be retooled to include the vents. This retooling procedure is very time consuming and very costly.
The present invention provides an alternative to the vents which is more reliable and less expensive.